Flight calculator for airplanes



Nov. 14, 1950 -J. E. FREr-:HAFER FLIGHT CALCULATOR FOR AIRPLANES 6 Sheets-Sheet 1 Filed Nov. l2, 1947 MEE zo M O QJrHm E zo STE@ @ma MEE. nog

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IN VEN TOR., 72M@ 6 W.. M` Qn m di n NN; E E E. mw Nwmm m i t J QN. lmI-L NOV 14, 1950 J. E. FREEHAFER 2,529,601

FLIGHT CALCULATOR FOR AIRPLANEs Filed Nov. 12, 1947 6 sheets-sheet 2 FIG.. 6.

WHEN PLANE CALLED T0 LEAVE .STACK HERE MIN. HOLDING LOOP I S REQUIRED 1mm RUN WAY HOLDING LOOPD l 1D H wHEN P ANE CALLED TOLEAVE .STACK HERE MAXHOLDING LOOP 1s REQUIRED I: 7 Y CALE- j la. 1MIN=OINCHE5 OE TAPE DRAWN /ZDIZE 2x=.155 MIN, No WIND Q`ANELE=O DRTETANOLE=O WIND 24 MPH DFTANGLE GROUND COURSE OR TRACK AIR SPE ED G AND HEADING ROUND FEED PLANE AIR .SPEED 120 MPH.

l A5 IN VEN TUR.

//w ATTORNEY Nov. 14, 1950 J. E. FREEHAFER 2,529,601

FLIGHT CALCULATOR FOR AIRPLANES Filed Nov. 12, 1947 6 Sheets-Sheet 3 FIGI. 4 @ROUND LEET WIND 3 7/CouRSE of STACK LOSS TIME= AIRPIANE 2.1% MIN. E 2 N 5 1 OT RUNWAY Q COURSE W 0 v E NWN n3 a 14 1S 12 11 1o S a 2970 6 Y AIRPLANE WIND g COURSE WITH -Sf- 1T RE PECT To o Y Q o CONTRUCTION oF/IovINe ,IRD ODI 31 LNEQQPALLELTOQUNWAYCOURSE Fl 6.16. L l 5 AIRPLANE COURSE WITH G RESPECT To DoDY 0E MovI NC AIR GROUND COURSE RICHT WIND STACK LOSS TTME= E 2.1% MIN. J+S

oS \0EAIRPLANE Amm 2o o A. .LINE PARALLEL WIND To RUN WAY I COURSE I W COURSE' E RUNWY RUN] AYr f IB 0B FIGLIO.

L=LENGTH oEARM CONSTA NT SUCHAS @INCHES/MIN.) PWIND SPEEDl l=PLANE SPEED 1 1; =HoLDING LooP TIME T= ToTAL TIME QSSTACK LOSS TIME OR L: CLSC-M C #N VEN TOR. l BY @auf ma 0.5 1.o 1.5 2.o 2S STACK LoSS TIME IN MINUTES w ATTORNEY RATIO OF WIND SPEED TO AmPLANE AIR SPEED Nov. 14, 1950 J. E. FRI-:EHAFER 2,529,601

' FLIGHT OALOULATOR FOR AIRPLANES Filed Nov. 12, 1947 6 Sheets-Sheet 4 LEFT WIND `STACK 1.055 TIME 2.1961 MIN.

RuNwAY GROUND COURSE 1 N-TIME COURSE HEADING HEADING7 0B MAGAZIMUTH=55I9 4*/- Am COURSE /LEZf-'ILIVTISDNGNETIC PARALLEL To RUNWAY COURSE HEADING Fl 6.13. BELT VLND STACK LOSS TIME 2.196 MIN.

AIRcOuQsE RIGHT WIND MAGNETIC HEADING KA/IUTHMG GROUND/COURSE HEADING IwNwAY 5g 6. INVENTOR. l WAZ. /Z/z, /w ATTORNEY Nov. 14, 1950 J. E. FREEHAFER 2,529,601

FLIGHT cALcULAToR FOR AIRPLANES Filed Nov. 12. 1947 l 5 sheets-sheet 5 145 140 11 ;-...f 114 142 m 141144 120 :s311145 12s 127 la 100 BY 6' `9fIN V EN TOR. I @14 @i 4 ATTORNEY Nov. 14, 1950 J. E. FREEHAFER 2,529,601

FLIGHT CALCULATOR FOR AIRPLANES Filed Nov. 12, 1947 6 Sheets-Sheet 6 FIGZ.

GROUND COURSE OF AIRPLANE TOTAL TIME OF HOLDING LOOP DRIFT ANGLE 1/f ACTUAL LOOP F1624. LENGTH L= @L Am COURSE SIMULATED LOOP OF AIRPLANE LENGTH L: QI

THus LENGTH L1: U5)

DRFTANGLE FIGZZ.

LOOP CORD CLUTCH INVENTOR.

| f BY W( we me W Q LK 212 sLIDE 'vv I@ /M/ ATTORNEY Patented Nov. 14, 1950 ,zeigen FLIGHT CALCULATOR FOR AIRPLANES John E. Freehafer, Rochester, N. Y., assignor to General Railway Signal Company, Rochester,

Application November 12, 1947, Serial No. 785,422

16 Claims. 1

This invention relates to calculating organizations for computing the time and direction that an airplane must fly under various conditions to consume different specified times in a landing procedure, and more particularly pertains to a computer based on a moving coordinate system correlated to a fixed coordinate system.

This invention is to be considered in the nature of an improvement over the disclosures in the prior applications of Saint Ser. No. 569,335 filed December 22, 1944, now Patent No. 2,495,139, and also the prior application of Field, Wight and Hewes-Ser. No. 573,876 iiled January 22, 1945, now Patent No. 2,522,029.

When a number of airplanes approach an airport ready to land at the same time, these airplanes are assigned to different altitudes of a storage or holding stack near an airport, and are then instructed to land one at a. time at spaced intervals. In other words, the airplanes are held in a stack with each one ilying at a diierent altitude. The controller instructs the airplane in the lowest altitude of the stack to begin a landing procedure, which instructions are followed by successive instructions directing the remaining airplanes to each descend to the next lower altitude of the stack as soon as the next lower altitude is vacant. In this way, the airplanes are laddered down in the stack so as to bring the airplanes successively t the lowest altitude to perform landing procedures one at a time at spaced intervals.

It will be apparent that the controller is unable-to know the exact location of an airplane in the lowest altitude of the holding stack when he instructs it to make a landing procedure. For this reason, it is practically impossible for a controller to cause` the airplanes to land at equally spaced intervals to obtain the greatest landing efciency even though he may call or instruct the airplanes to land at equally spaced intervals.v

` In accordance with the present invention, it is proposed that the landing` procedure for each airplane shall include the ying of a holding loop having a length dependent upon the time that it took such airplane to leave the holding stack following the reception of its instructions to perform a landing procedure. Thus, if successive airplanes are instructed at equally spaced intervals to perform their landing procedures, then the actual landings will occur at equally spaced intervals. This is because each landing procedure includes a variable length holding loop which compensates for the loss of timedue to the location that the airplane occupied in the holding stack when receiving instructions to land.

One object of the present invention is to provide a computer for calculating the time and the direction that an airplane must fly for a holding loop in the above described landing procedure under any given conditions, which computer is organized on mathematically accurate postulates, and performs its operations by apparatus giving mathematically correct solutions.

It is readily apparent that diiferent wind conditions will prevail at different times, so as to make4 it necessary'to provide a calculating organization which takes into consideration such wind conditions in a manner to give accurate calculations of the direction and times involved. Thus,A another object of the present invention may be said to reside in the provision of simpleand accurate means for taking into consideration the various conditions of windage. Generally speaking and without attemptingy to define the exact nature of the present invention, this last named object is effected by the provision of a computer which takes advantage of twoseparate coordinate systems of calculations, one of which is fixed and the other of which moves with the body of air in which an airplane is iiying.

Another object of the present invention resides in the provision of apparatus to automatically compute the times and directions involved in a holding loop after the basic factors involved have been set into the apparatus in part manually and in part automatically.

Other objects, purposes, and characteristic features of the present invention will be in part obvious from the accompanying drawings and in part pointed out as the description of the invention progresses.

In describing the invention in detail, reference will be made to the accompanying drawings in which like reference characters designated corresponding parts through out the several Views, and in which:

Fig. l is a front view of one form of a calculator. or computer constructedy in accordance with the principles of the present invention for calculating the directions and times involved in a holding loop under various conditions;

Fig. 2 is a top View of the computer illustrated in Fig. 1;

Fig. 3 is a fragmentary sectional View of the computer of Fig. l taken on line 3-3 of Fig. l;

Fig. 4 is afragmentary view of the tape windingmechanism taken on lines 4-4 of Fig. 2;

Eig. iis an enlargedview of the `tape and the scale thereon as seen in its position at which it is read to give the calculated out-time;

Fig. 6 illustrates one form of landing procedure pattern with which the present invention may be employed;

Fig. 7 is a graphic illustration of diierent holding loops under no-wind conditions;

Fig. 8 is a diagrammatic illustration of the dial D in the position to which it should be positioned for no-wind conditions illustrated in Fig. 7;

Fig. 9 is a graphic illustration oi one manner of calculating a drift angle for a particular wind condition;

Fig. l is a chart for use in connection with setting the wind slide W both in Fig. 1 and in Fig. 17;

Fig. 11 is a graphic illustration of a holding loop under a 20 percent left wind with a stack loss time of 2.196 minutes;

Fig. 12 is a diagrammatic illustration of the dial D in the position to which is should be positioned for the particular wind conditions illustrated in Fig. 11;

Fig. 13 is a graphic illustration of a holding loop under a 20 percent right wind with a stack loss time of 2.196 minutes;

Fig. 14 is a diagrammatic illustration of the dial D in the position to which it should be positioned for the particular wind conditions illustrated in Fig. 13;

Fig. 15 is a graphic illustration showing the relation between the course of an airplane in the moving body of air relative to the ground course for that airplane under the wind conditions illustrated and discussed in connection with Fig. 11;

Fig. 16 is a graphic illustration showing the relation between the course of an airplane in the moving body of air relative to the ground course for that airplane under the wind conditions illustrated and discussed in connection with Fig. 13;

Fig. 17 is a front view of a second form of a calculator or computer constructed in accordance with the principles of the present invention for calculating the directions and times involved in a holding loop under various conditions with certain automatic features of operation not disclosed in connection with Fig. 1;

Fig. 18 is a top view of the computer illustrated in Fig. 17;

Fig. 19 is an enlarged and expanded view of certain parts included in the wind slide mechanism |65 of Figs. 17 and 18;

Fig. 20 is a partial back View of the computer panel illustrated in Figs. 17 and 18, showing more particularly the driving mechanism;

Fig. 21 is a fragmentary back view of the electromagnetic brake for the cord holding mechanism of Figs. 17 and 18:

Fig. 22 is a diagrammatic illustration of control circuits suitable for the computer structure ilustrated in Figs. 17 through 21; and

Figs. 23 and 24 represent respectively the ground course and air course of an airplane, which courses correspond to those illustrated in Fig. 15, but which have applied thereto the system of notation employed in the mathematical analysis of the ilight problem involved.

Holding stwck umd holding lobps With reference to Fig. 6 of the accompanying drawings, it will be observed that a runway has been indicated to the left of a holding stack dened by suitable inner and outer beacons IB and OB respectively. These beacons are assumed to be of any suitable type, but are preferably radio beacons which are in line with each other and the landing runway in such a way that an airplane in approaching the runway from the right, Will be able to properly locate the landing runway and employ the glide path provided by suitable apparatus associated therewith. In other words, the present invention contemplates that its highest usefulness will be in connection with the directing of airplanes in landing procedures that are to be effected whil-e flying blind due to adverse atmospheric conditions.

The holding loop A designated by a suitable legend in Fig. 6, is formed by straight lines connecting the outer beacon OB with a standard procedure turn or semicircle. This holding loop A, is the minimum sized holding loop, while the holding loop B is the maximum sized holding loop, it being understood that the holding loop for any particular ight may be of some intermediate size dependent upon the stack loss time for that particular flight. For the purpose of the present disclosure, it is assumed that the diagram represents iiying times rather than distances.

which can be done since a standard speed must be selected for the various airplanes expected to use the holding stack and associated holding loops, and this selected speed must be maintained constant throughout a landing procedure. With these assumptions the semi-circular portions of the holding stack are assumed to consume one minute flying time each (i. e. three degrees per second), while each of the straight legs of the holding stack are assumed to consume one and one half minutes iiying time. It should also be understood that an airplane may enter a selected altitude of the holding stack from an associated airway at any point in the holding stack.

It is contemplated that each of the different runways of an airport will have suitable inner and outer beacons 1B and OB associated therewith so as to provide aV holding stack for that runway when the wind conditions require use of that runway.

Airplanes are assumed to ily in the holding stack and in the holding loops as indicated by suitable arrows in the diagram in Fig. 6. If an airplane is called from the holding stack while it is passing over the inner beacon IB, it continues its course around the stack by making the one minute semicircular procedure turn and then passes over the outer beacon OB. When the airplane passes over the outer beacon OB, the pilot or the airplane reports to the controller Who then through the medium of the calculating apparatus provided in accordance with the present invention advises the pilot as to his heading. The airplane then proceeds at constant speed at thev given heading and after a given time, conveniently termed the out-time represented by the line between OB and P, which is also calculated by the computer of the present invention, the controller instructs the pilot to begin a right hand procedure turn which is of the same type as the procedure turn of the holding stack i. e., three degrees per second. The pilot of the airplane continues on the procedure turn, until his airplane comes onto a line defined by the outer beacon OB and inner beacon IB at which time he proceeds on that straight line from the point P2 toward the runway as directed by the beacons. It will be noted that the procedure turn from the point P to the point P2 is slightly greater than a semicircle, and the excess consitutes two equal segments X. The semicircle is dened by a diand suitable arrangements may be provided for covering the'moving parts with only the necessary dials and adjusting means open to the view of an operator. Also, on this panel in a suitable freev space is the abbreviated operating rules for using the computer.

The Q angle setting lever II is pivoted by a suitable pin I entering the support member I 5 as best seet in Figs. 1 and 3. This support mem ber I6 is a U-shaped piece securely mounted to the' panel I0. A circular slot Il is provided in the panel I0 to receive a bolt I8 with an enlarged head in back of the panel I0 and a thumb nut in 'such a Way as to be movable through the slot I1 while the thumb nut is loosened, but adapted to hold the Qangle lever in any position in which it is setk When the thumb nut of the bolt I8 is tightened. f

On the face of the panel Ill around the circular slot I1, and around a semicircle inscribed by the pointer I9 at the end of the Q angle lever, a scale of degrees is provided. The center point of this scale is designated zero and represents the point to which the arm II is set when there is nowind conditions to enter into the calculations. The remaining portions of the scale on either side of the zero point are calibrated in equally spaced degree marks up to 90 to complete the semicircle. These degrees represent the right and left values of the Q angle which is found as Will be later described, but which on the opening chart is brieily dened las the wind angle minus the drift angle. The wind angle is the acute angle between the direction of the ground course` on the approach to the runway and the reciprocal of the Wind direction. The drift angle is the acute angle between the direction of the ground course and the direction of the axis of the airplane on the approach to the runway in the landing procedure (see Fig. 9).

TheQ angle lever is illustrated as having a slot substantially throughout its free end in which is mounted a slidable wind setting member 2| that can be set in any position along the slot 20 'and held there when the thumb nut 22 is tightened. Along the face of the lever I I is a scale calibrated with equal increments beginning from the pivot point I5 and extending outwardly along the free end of the lever II. The slidable member 2| has a projection 23 which is adapted to have the tape I2 pivotally attached thereto by asuitable pin 24, as best seen in Figs. 2 and 3. The extending portion 23 is adapted to permit the point 24 at which the tape I2 is attached, to be set exactly over the pivot point I5 of the Q angle lever II when the slide 2| is in its zero position as indicated by the index or pointer 25 on the zero setting of the scale on the face of the lever II.

Before discussing the spring biased tape holding mechanism THM and the idler pulley 26, it should be noted that the ilexible tape I2 may be of suitable length, but its length as selected, is calibrated in accordance with the maximum holding loop dimensions with which the computer is to be employed. For example, the maximum holding loop selected for the purposes of the present disclosure, is assumed to represent a maximum of 5.696 minutes, and for convenience, it is assumed that six inches of flexible tape are provided for each minute. However, it should be clearly understood that any suitable scale may be employed. That is, one inch of the tape may represent one minute of the holding loop, or any number of inches or fractional portions of inches may be assigned to represent a minute of the holding loop. In any event, and in accordance with the particular scale selected, the length of the tape from the pivot point 24 (when exactly positioned over the pivot point I5) to the read-out of the stack loss time setting means SLT, represents the total holding loop time. Also,-

in accordance with the same scale of inches per minute of time, the diameter of the supporting pulley or wheel 21 represents a standard two minute procedure turn for an airplane.

Assuming a scale of six inches per minute, then thepulley 2l will have a radius of 1.91 inches insidev of its guide flanges. Considering that the tape I2 extends from the point I5 over the pulley 2l is returned to the point I5, it will be seen that the tape then represents to a time scale the actual maximum holding loop (assuming the mechanism THM to be in its right hand biased position), as above described in connection with Fig. 6. But it is inconvenient structurally to return the tape I2 to the pivot point I5, so that an idler pulley 26 is provided to cause the tape I2 to leave the pulley 2l on a tangent line passing through the point I5, but sothat the end of the tape can pass through a stack loss time setting means SLT. The stack loss time setting means SLT comprises a tape holding device including a thumb nut 28 which may be tightened to clamp the tape I2 for holding it, or which may be loosened to permit the tape I2 to be moved to a different position by the handle piece 29 attached to the end of the tape, and also a readout which is indicated by the arrow and is conf veniently referred to as stack loss time read-out SLT.

The tape holding mechanism THM includes a bearing and support member 3Il, which will freely slide in the slot 3|, and is maintained in position by reason of suitable guide portions on each side of the member 3D. This member 30 is rectangular so as to be non-rotatable. This slot 3I is parallel to a line drawn from the center I5 tangent to the pulley 2l, and in part dened by the tangent portion of the tape I2, An extending shaft 32 is attached to slide member 30 and has a coil spring biasing pulley 33 mounted thereon. This pulley 33 is mounted on the pivot 32 to rotate, but when rotated in a counter clockwise, it is biased against such rotation by a suitable coil spring 34. On the outer periphery of this pulley 33 is attached a flexible cord or tape 35 which iswound around the pulley and attached to the panel at point 36. Thus, if the tape I2 is shortened, the holding unit THM is moved t0 the left tightening the spring 34. But if the tape I2 is lengthened, the spring 34 tends to wind up the cord 35 and move the holding unit THM to the right to keep the tape I2 tight and also to properly position the pulley 21 representing the standard procedure turn of a holding loop and mounted on' the shaft 32.

Extending around these two-pulleys 21 and 33 on one side is a holding' member 3l which serves to support the outer end of the shaft 32 and carries a pointer 38 designating the relative position of a' dial D which is pivotally mounted on the shaft .32 and is manually positionable to represent the azimuth of the run-way plus the drift angle in a manner later to be discussed. When positioned, the dial D is held by a spring biased retention means 44. In other words, this dial D has a scale around its circumference divided into equal increments representing 360.

An -angle indicating member 39'is pivoted on the shaft 32 with an extending pointer `P attached to provide readings from the scale of the dial' D. The upper `portion of this member 39 is bent so as to cover a portion of the tape as viewed in Figs. 2 and 5 to provide a read-out designated by a suitable arrow and the letter T from which the out-time may be read from the tape I2. This extending portion of the member 39 has a U- shaped extension l0 which vpasses around the tape I 2 in such a Way that the pointer P is moved to different angular position in accordance With the angle at which the tape I2 enters the'pulley 2`I. The read-out at T thus provides a value on the scale of tape I2 which falls at the point of tangency of the tape I2 on the pulley 21. The pointer P is parallel to the line of tangency formed by the tape I2.

The upper side of the tape I2 has a scale indicated thereon having increments representing time (see Fig. 5). This scale has its zero at the point 24 and runs up to a value slightly greater than the maximum out-time required.

, The underside of the tape I2 has a scale indicated on it with increments also representing time. This scale has its zero at the stack loss time read-out SLT when the tape is positioned to represent the maximum holding loop as above described. The scale increases from zero along the tape up to a value to represent the maximum stack loss time, whichfor the values assumed is equal to 2.5 minutes.

It should be noted that the wind slide W may be moved to any point along its scale, and in some cases may assume its outer position at the Same time that the lever II is moved to a ninety degree right Q angle. Since the idler pulley 26 must be sufficiently to the left with respect to the location of the tape holding mechanism THM to provide proper tangency for the tape I2 when the -tape holding mechanism THM is moved to its extreme left hand position, it is necessary for the tape I2 between point 24 and pulley 2l to be ina different plane than the outer surface of the idler pulley 26 under the wind conditions above mentioned. This is possible because the idler pulley 26 is off set as seen in Fig. 2 to allow for such an operation.

Operation of primary computer I et us assume that there is no wind. Under such conditions, there are certain settings of the computer that are fixed and may be made before an airplane is to be called from the holding stack. More specifically, the lever II is set to designate a Q angle of zero. Also, the wind slide member W is moved to its zero position. The dial D is set with respect to the pointer R to designate the azimuth of the landing runway. We may now assume that an airplane is called from the holding stack (see Fig. 6) while passing over the inner beacon IB. The airplane continues to y the holding stack course so as to pass over the outer beacon OB before proceeding to fly a holding loop pattern. The pilot of the airplane reports while passing over the beacon OB, so that the controller by using a suitable Watch, or other timing device, may determine the elapsed time between the initial call for the airplane to leave the holding stack and the time that the airplane reports passing over the outer beacon OB. This elapsed time is conveniently termed the stack loss time. The controller now operates the computer of Fig. 1 to obtain the out-time of the holding loop and also to obtain the magnetic azimuth of such out-time course. Thus, all that is necessary to be done when the stack loss time is known, is to loosen the thumb nut 28 and move the handle 29 so as to move the flexible tape I2 until the stack loss time read-out SLT designates the particular stack loss time for that particular night. In the present case, the stack loss time wouldbe two and one half minutes. Since the stack loss time has been set into the computer, the out-time may be readfrom the tape at theread-out T, while the magnetic azimuth of the out-time course may be read from the read-out P on the dial D. With the conditions assumed, the out` time will be one minute, while the out-time course forms an angle of 35.3 degrees with re'- spect to both the in-time course and the runway course, since these two courses coincide when there is no wind. This holding loop for these conditions has been illustrated in Fig. '7.

Assuming the runway course to extend north and south with the landing of the airplane being made towards the north, the azimuth of the runway will be 360 degrees (N), so that the magnetic azimuth of the out-time course will be 144.7 degrees, as read from the dial D at the read-out P. This setting of theA dial' D and the position of the pointer P has. been illustrated in Fig. 8. This particular setting of the calculator is for a holding loop which corresponds to the minimum holding loop A described in connection with Fig. 6.

With reference to Fig. '7, it Will be noted. that a holding loop hasl been diagrammatically indicated for a stack loss time of 1.563 minutes. In other words, the positioning of the handle 2Q so as to move the flexible tape I2 to give a stack loss time read-out of 1.563 at the read-out SLT, allows the tape holding mechanism THM to move to the right as seen in Fig. 1, causing the pointer P to move to a new position and the read-out T to give a` new out-time. In this case the outtirne will be. 1.5 minutes and the out-time course angle vwith respect to the runway course and intime course will be 24 degrees. The magnetic azimuth of the out-time course is thus 156 degrecs.

Likewise, Fig. 7 illustratesV the holding loop when there is no stack loss time whichisset into the calculator at ther read-out SLT.v vThis gives an out-timev of 2.3 minutes and an out-time course angle of 15.7 degrees with respect to the in-time and runway courses. Assuming the same settings for the dial D we rind that the magnetic azimuth of the out-time course is 164.3 degrees.

From the above description and typical examples, it will be readily understood. that the setting of any given stack loss time at SLT will give a proper holding loop so that the corresponding out-time may be read from the read-out OT, and the pointer P will give the magnetic azimuth for the proper out-time cours-e belonging to such holding loop. Obviously, there are just as many different holding loops as there are different stack loss times varying from zero to two and one half minutes for the particular values assumed.

In still air, the lapse of time and the distance of movement of the airplane vary directly with each other because the speed of flight is assumed to be constant throughout the landingV procedure. Because of this relationship between time and distance, the contour of the flexible tape for a particular setting represents in miniature the actual ight course of the airplane bothV with respectto the ground and with respect to the ii body of air through which it is flying even though the length-'of the tape l2 is considered to represent time.

When an airplane is ying under wind conditions, it is flying in a body of air with respect to which it .has a particular contour of flight;

but since the body of air is moving with respect to the ground, such contour ofr` flight is also moving with respect to the ground. This produces a distinctly .different contour of flight with respectto the ground. It should be apparent that if a given circular co-urse is to be traveled by an airplane :with respect to the ground, that suchfcourse will not be circular with respect to the moving body oi air. Similarly, if an airplane is to flya circular course with respect to the moving body of air, such course will not be circular with respect to the ground.

The present invention is based upon the provision of a moving coordinate system considered with respect to the moving. body of air which moving coordinate system is properly related to the stationary ground coordinate system. With this as a basis, it is possible to simulate and calculate the actual flight course in air under wind conditions because such course is geometrically simple; and this simulation and calculation of the course in the moving body of air can be used to give the actualmagnetic headings and time values involved when properly correlated to the xed ground coordinate system. The primary computer of Fig. 1 has the flexible tape I2 positioned to simulate the air course of the airplane with respect to the moving body of air; and this air course is related to the ground coordinate system through the setting of dial D, which involves the calculation 'of the drift angle for the airplane with given wind conditions.

The process of calculating a drift angle is well known, and may be facilitated by the use of simple computers such as shown in the prior patents to Prall. No. 1,428,449, C01V11 N0. 1,910,093 0r Thurston 2,296,692. However, for the purposes of making the present disclosure complete, Fig. 9 illustrates one-manner of calculating a drift angle. For the purposes of this illustration, it is assumed that there is a wind having a speed equal to twenty per cent of the air speed of the airplane and a direction forming a forty-five degree angle with the ground course or runway. This Wind direction is shown as a wind coming from the left of the airplane ground course. For a wind coming from the right of the airplane ground course, the construction of Fig. 9 would merely be reversed.

Referring to Fig. 9, the direction and velocity of the moving air body is indicated vectorially by the vector w forming a 45 angle with the ground course, and the magnitude of this vector w is the radius of a wind speed circle WS. The air speed of an airplane is represented by the radius of an air speed circle AS. By drawing a line parallel to the ground course from the point where the negative wind vector -w intersects the circle WS, and then drawing another line from the centerof the circles to the point where such parallel line intersects the air speed circle AS, it is possible to thus produce a vector diagram giving the ground speed over the ground course and also giving the proper heading of the lairplane to following the ground course. This heading angle is known as the'drift angle of the airplane with respect to the ground course. For' the purposes -of the drift anglejcalculation shown in Fig. 9, it is assumed that the'wind speed is twentyper cent of the air speed of the airplane, as for example, the Wind speed maybe 24 miles per hour when the cruising speed of the airplane is miles per hour. It should be understood however, that the vectors assume the same positions and the same relative magnitudes so long as the ratio between the two speeds remains the same. In the particular drift angle calculation shown in Fig. 9, the drift angle is found to be 8.1, while the Q angle (which is the wind angle minus the drift angle) is found to be 36.9".`

. When the drift angle has been determined, it is set into the computer of Fig. l by moving the dial D to the azimuth of the runway plus or minus the drift angle depending upon whether the wind is coming from Athe right or from the left with respect to the ground course of the airplane toward the runway. When the wind is coming from the left of the ground course, the drift angle is subtracted from the azimuth of the runway as illustrated in Fig. 12, which shows the dial D enlarged to illustrate the typical setting just explained. On the other hand, if the wind is coming from the right of the ground course, then the dial D is set so that the drift angle is added to the azimuth 'of the runway as typically shown in Fig. 14. y

As above explained, the calculation of the drift angle, as in Fig. 9, also gives the Q angle which is set into the computer by loosening the thumb nut I8 and moving the pointer I9 to the proper position for the calculated Q angle. If the wind is from the left side of the ground course, as indicated in Fig. 9, the Q angle is in the lower quadrant designated in Fig. 1 left Q angle. On the other hand if the wind is from a direction on the right side of the course, the Q angle is in the upper quadrant in Fig. 1 designated right Q angle.

Let us assume that an airplane is called from the holding stack and proceeds over the outer beacon OB, at which time the pilot reports to the controller. By suitable timing means, the controller determines the elapsed time between his callv to the plane instructing it to leave the holding stack, and the time that it reports as passing over the outer beacon OB. The controller then immediately sets this stack loss time into the computer of Fig. 1 at the stack loss time read-out SLT. With a knowledge of the stack loss time and the percentage of the wind velocity, the operator can read from the scale L on the chart of Fig. 10, the setting for the 'wind slide W. With these settings made, the` operator can read the magnetic azimuth of the out-time course from the read-out P on the dial D which the controller immediately transmits to the pilot of the airplane. The controller can also read the outtime from the scale on the tape at the read-out T, which represents the time which should elapse after the pilot reports over the outer beacon OB before he begins his procedure turn. When this out-time has actually elapsed, as measured by a suitable time measuring mechanism, the controller then instructs the pilot of the airplane to begin the procedure turn. The pilot of the airplane proceeds on the procedure turn until the airplane is on a course in line with the ground course to the runway as defined by the outer beacon OB and the inner beacon IB. Because the in-time course IT (see Fig. l1) is tangent to the procedure turn7 the airplane has a proper heading when it reaches the point of tangency to follow this in-time course. Since the in-time course is at the drift angle for the particular culation of drift angle or the like, and some dil rectly underthe controlling guidance of any instrument landing facilities.

As an example of the operation of the computer under left wind conditions, Fig. 1l graphically shows the air course oi' the airplane assuming a stack loss time of 2.196 minutes and the ratio of wind speed to airplane speed to be twenty per cent. By referring to the chart of Fig. 10, it will be found that for this stack loss time and air speed ratio, the setting of the slide W is 4.2 (indicated by dotted lines in Fig.

As above described, the length of the tape I2 of Fig. 1 represents the time during which the airplane is flying the holding loop. During this same holding loop time, the body of air is moving in a direction assumed in the drift angle calculation of Fig. 9 to be at 45 from the runway ground course. Since the Q angle is set into the computer of Fig. 1, the position of the lever I I represents the actual direction of the Wind with the simulated holding loop assuming a proper relation thereto. Since the movement of the body of air in the direction represented by the position of the lever II is at a different speed than the speed of the airplane, the length of the lever employed to represent the air movement must be different than the length of the tape I2 although the position of the slide W also represents a time corresponding to the holding loop time. The distance of air movement bears the same relation to the length of the holding loop as the speed of the wind bears to the speed of the airplane. the scale position of the slide W is determined by multiplying a constant, such as six inches per minute, by the percentage of wind and the time of the holding loop. This is mathematically ndicated by the notations of Fig. 10, while the chart is used to facilitate the actual calculation. Assuming the constant factor of six inchesper minute, then the reading 4.2 obtained from the chart of Fig. l0 may be interpreted as 4.2 inches.

Referring to Fig. ll of the drawings, it will be noted that the holding loop is drawn to show the course of an airplane in a moving body of air. The body of air may be considered to be a wind that is traveling in a direction represented by the arrow designated a left wind. A point in this moving body of air, such as the point designated CB1, travels in a direction towards the outer beacon OB during the flightrof the airplane through the holding loop. Assuming that the wind has a particular speed relative to the speed of the airplane, then there is some. point in the moving body of air that will move toward the outer beacon OB, during the passage of the airplane through the holding loop,- and just pass over the outer beacon as the airplane is returning to the outer beacon OB. Assuming a particular ratio between the wind and airplane speeds, such as twenty percent, then the distance that the point OBl in the moving body of air travels during the flight of the airplane through the Vholding loop bears the same relation to the distance through the holding loop as does the speed of the wind bear to the speed of the airplane. In other words, the scalar length of the line between OB1 and OB represents the time of travel of the moving body of air; while the scalar length of the holding loop (including the outtime OT, 2X, the one minute semi-circle, and the inl-time IT) represents the time of the airplane in making the holding loop. Obviously, since ThllS,

lspeed of the airplane.

14 the wind is assumed to be travelling ata slower vspeed than the airplane, the increments ottime marked off on the line CB1-OB, are smaller than the increments of time marked off on-theholding loop. This graphic illustrationV of Fig. 11 has indicatedthereon the various values of'time, directions and angles involved in a holding: loop under the conditions assumed, which valuescorrespond to the values given by the computer Vwhen the various assumed settings are placed into the computer. y A

It is noted that the computer-dial D is so set that the in-time represented by the lower-'portion of the tape I2 (i. e. portion beneath the pulley 2'I) is in effect positioned in accordance with the magnetic azimuth of the runway course (see Figs. 1 and l2). The out-time course and direction is indicated by the position of the pointer P, so that the degree to whichV it is displaced from a center line-passing through the read-out R gives the angle between the out-time course andl the in-time course. But since the actual magnetic azimuth of the out-time course-is desired, the drift angle is inserted into the setting of the dial D. Referring to'Fig. ll, it willbe noted that the ground course heading is vin a clockwise position with respect to the air course heading for the in-time course.v Thus, itshould be apparent that thedrift angle should be' subtracted from the azimuth of the runwayfas shown in detail by the dial setting illustrated in Fig. 12. With the dial D set with the drift angle subtracted from the azimuth of the runway course, the pointer P actually assumes a position giving the magnetic heading of the out-time course with respect to the dial D.

For the purpose of making clear the relation between the moving coordinate system and the fixed coordinate system associated with vvthe ground, Fig. 15 is provided with a graphic illustration of how the ground course may be con'- structed. In this Fig. l5, the same holding loop shown in Fig. l1 is included as associated with a runway. It might be noted that the designation 36 at the end of the runway means that the contact point for an airplane at thaitend of the runway is for a ground course having a magnetic azimuth of 360 from due north, or is in fact north. The designation I8 at the end of the runway means that the contact point for alariding airplane at that end of the runwayis for a ground course having a magnetic azimuth 180 from due north, or is in fact south. j

As above mentioned, the distance between OB and OB1 is proportional to the length ofthe holdingloop. Since both the holding loop` and this line between OB and OBl represent time, both the holding loop and the line between OB `and OB1 may be divided into an equal number of time segments. Each time segment of the line OB-,OB1 will represent the same period of time as .each

.time segment of the holding loop, -but will have a length bearing the same relation to thelength ofsuch segment ofthe holding loop, as the velocity of the moving body of air holds to Vthepair In Fig. 1,5, the holding loop is divided into fourteen equal time segments. Likewise, the line OB to OB1 is dividedinto the same Vnumber of equal time segments. Let us assume that an airplane leaves the outer beacon OB and reaches the -end of the rst segment in the time represented by the-length of such segment. Then it will be noted that the moving body of air has moved a `distance proportional to the irst segment of the line between OB and OBl,

so .that the airplane is actually locatedl over the ground at apoint along a line parallel to the line between OB and OB1 `a Vrdistance from the air course lholding loop equal to the `length of the lirst segment of the line OB and OBl. Similarly, asthe airplane proceeds along the holding loop tothe-gend of each of the successive segments marked off on the holding loop, the airplane is actually over the ground at a point represented by a distance away from the represented holding loop corresponding to the distance represented `by the end of the correspondingly numbered segment of the line OB-OB1. These different points connected rby a dot-dash line represent the actual ground course of the airplane. This Fig. 15 illustrates that the airplane in making its righthand procedure turn, follows a course which is circular with respect to the moving body of air, but which is not a true circle with respect to the ground. Also, the airplane in following the air course is given accurate information in accordance with the computer of the present invention so that as it performs vthe procedure turn and comes into line with the outer and inner beacons OB and IB, it has the proper heading to -proceed on a straight ground course to reach the runway. In other words, the ground course fior therunway is tangent to the procedure turn, andthe pilot of the airplane does not have to compute a drift angle for the in-time course because vthe airplane is properly headed for the then existing conditions of the wind. This would not beV true if the runway course was not an exact tangent to the procedure turn.

As an example of the operation of the computer under right wind conditions, Fig. 13 graphicallyshows the course of the airplane in the movving body of air assuming a stack loss time of 2.196 minutes and the ratio of wind velocity to airplane speed to be 20 per cent. In other words, the assumptions for the holding loop course of Fig. 11 except that the wind is assumed to be coming from the right side of the ground run.- way course as the airplane is landing. The position of the slide W remains the same, i. e. in

the position 4.2 as obtained from the chart'of Fig. 10. In this case the Q angle is 36.9 in the upper `quadrant; designated Right Q angle.

By referring to Fig. 13, it will be noted that the air course heading for the in-time courseis located in a clockwise position with respect to the ground course heading. This means that a similar relationship should be included in the setting of the dial D, which is effected by adding the drift angle to the azimuth of the runway. Referring to Fig. 14, it is noted that the dial D is thus set to 8.1". Y

In considering the holding loop represented in Fig. 13, the procedures With respect to the airplane will be omitted, since the controller and pilot communicate in the same manner as previ- -ously described. The computer is further set to vthe stack loss time of 2.196 minutes at the computer read-'out SLT. With these settings in the computer, the read-out T gives an out-time OT 'of .923 minute; while the pointer l? gives a magnetic azimuth of 120 for the out-time course heading.

In Fig. 13, the values'of 2X and the in-time IT Iare also given in addition to the standard one minute semicircleY The addition of these various times constituting the holding loop, gives a total holding loop time of 3.5 minutes which will be found to be the difference between the total 16 time 5.696i`inutes and the stack loss time 2.196

minutes.

-It will be noted from the holding loopk course illustrated inFig. 13, that the airplane in proceeding from the outer beacon OB actually performs a course in the moving body of air which crosses itself before the airplane can return to the outer beacon OB for proceeding over the runway vcourse to land. This rather complex appearing air course actually produces a ground course as shown inFig. 16 which has `been constructed on the same principles as described in detail in connection with Fig. 15. Thus, the details of thev construction of Fig. 16 will not be given, it being sufficient to note that the ground course of the airplane is of a proper contour to cause the runway course to form a tangent to the procedure turn so that the airplane will have the proper heading when it comes into line with the outer and inner beacons OB and IB for the Wind conditions assumed.

Again referring to Fig. 6 of the drawings, it will be noted that the holding loops illustrated are under no wind conditions and are drawn with respect to the ground coordinate system, so that if a holding loop were to be drawn into Fig. 6, which represents the ground course of the airplane under the particular wind conditions assumed for Figs. 11, then the ground course loop of Fig. 15 would be employed. It should he understood that there is a large number of` different holding loops corresponding to the diierent combinations of wind conditions and stack loss times, and obviously all of these diierent combinations cannot be graphically illustrated in this disclosure. It is thought to be suicient to give the typical examples described above.

There is one other specic case which may be mentioned although no diagrams are shown for its conditions, and that is when the wind is a direct head-on wind having a direction corresponding to the azimuth of the runway. In such a case, it is apparent that there is no drift angle, and thus the Q angle setting is at zero. However, since there is a wind in the direction of the out-time course, it is apparent that the time for such course will be less than the time required Afor the in-time course. This is compensated for by the calculator, since the slide W must be positioned in accordance with the percentage of wind velocity compared to the air speed of the airplane. Thus, as soon as the controller knows the stack loss time, it can be set into the computer at the read-out SLT, and from the chart in Fig. 10 the setting of the slide W can be obtained.

The dial D having been set at the read-out R to correspond with the azimuth of the runway, the controller may now read the out-time at the read-out T and the azimuth of the out-time course at the read-out P.

Structure of secondary computer sho-um in Figs.

' 17 through 22 In these gures of the drawings, a secondary form of computer has been disclosed embodying the same principles of the present invention as .disclosed in connection with the primary computfer but having certain automatic features to save time and eiTort on the part of the controller.

For example, in this form of the present invention, it is not necessary for the controller to measure the stack loss time, since the computer actsautomatically to measure the stack loss time and insert its value into the computing organization. 'This means that lthe computer provides the proper azimuth reading as soon as an airplane passes the outer beacon into the holding loop Without any operation on the part of a controller. These various automatic features will be presently described in detail.

The secondary computer of these Figures 17 through 22 comprises a support panel |00, a Q angle setting arm I I, a. exible cord o-r cable |02, a Wind percentagey setting stop |03, a spring biased and electromagnetic cord holding mechanism CHM, a setting dial D, a wind percentage mechanism |05, and various control and operating devices.

The Q angle setting lever |0! is pivoted at |05 lby a suitable pin entering the support member |01 as best seen in Figs. 1.7 and 18. This support member |01 is a U-shaped piece securely mounted to the panel |00. A circular slot |08 is provided in the panel |00 to receive bolt |08 with an enlarged head in tho back of the panel |00 and a thumb nut on the face of the panel in such a way as to be movable through the slot |08 While the thumb nut is loosened, but adapted to hold the Q angle lever |0I in any position in which it may be set when the thumb nut of the l.

-bolt |09 is tightened.

Around the circular slot |08 and a semicircle inscribed by the pointer ||0 of the Q angle lever |0I, a scale of deg-rees is provided. The center point of this scale is. designated zero and represents the point to which the arm |0| is set when there is no wind condition to enter into the calculations (i. e. when there is no drift angle). The remaining portions of the scale on either side of the Zero point are calibrated by equally spaced degree marks up to 90. These degrees represent the right and left values of the Q angle which is found` by calculation as described in accordance with Fig. 9, or by other suitable computer means. This. Q. angle in brief is the difference between the wind angle and the drift angle as previously described in connection with Fig. 9.

The angle lever |535 is illustrated as having a slot iII substantially throughout its length in which is mounteda slidable setting stop |03 which. may be manually set in any position so that the normal positionof the wind slide mechanism is determined in a manner later to be described. This slide blocr- |03 is separate from the mechanism |05 and may be manually set in any desired position, but the mechanism |05 is considered to be drawn toward the end of the lever I0! and make an abutment against the stop |03y by reason of a spring holding mechanism H2 includingr a spring H3 fastened at I!!! at the end of the lever. lili.

driven so as to be drawn toward the point |05, but when released by the driving mechanism, the spring I i3 causes the mechanism |05 to again be drawn against the setting stop |03.

The cord holding mechanism CHM is very similar to the tape holding mechanism THM of Fig. 1. A bearing and support member |20 is adapted to slide within the slot |2| within the panel |00. Non-rotatably mounted to this member |20 is a shaft |22 upon which is mounted the spring biased pulley I 23, the cord supporting pulley |24, the dial |25 designated Dial D on its face, and the pointer supporting member |25.,V l

As will presently be Y A described. the mechanism |05 is at times motor A holder bracket |21 is also attached to the bearing and support member |20 and extends around the right oi the pulleys |23 and |24 as-viewed in Fig. 18 and then in backof the dial |25 soas to provide a read-out at R. Suitable spring biased 18 retention means is provided at |28 for thedial so that it will remain in the position to which it is manually set. K

The member-|26 has attached to it a pointer having P inscribed on its face. A contact holdingl member |29 is also-attached to member |26 and is adapted to holdY one end of a rod I 30 in such a manner as to allow the rod to slide through its holding support. The other end oi the rod |30 is pivoted about a hollow shaft |3| supported by the mechanism |05. In other words, the hollow shafty |3| provides a pivot for rod |30 which is thus held tangentl to the pulley |24 with-the same angle as the exible cord. |02. Afslidable member |32 is adaptedto move along the rod |30 ineither direction depending upon the movement-o1cv the cord |02 around the pulley I 24'. `This is because of the bead attachments |33 and 38. As the bead |33 travels to the right, it comes into contact with the arm member |34 and causes the slide |32 to move along the rod .|30 because the bead |33 cannot pass through the eyelet in the arm member |34. This moves the slide into position to push the movable contact |35 upwards as viewed in Fig. 17 so Vthat there is an electrical circuit closed between terminals |36 and |31 at just the time that the beadk |33 Varrives atthe point of tangency between the cord |02 andthe pulley 24. As the cord |702 is moved in a counterclockwise direction with. respect to the pulley |24, then the bead |38 contacts the eyelet of the member |34 and moves the slide |32 back to its initial position, which movement is'limited by the bead |33 coming into contact with the hollow shaft |3I.

As best ,viewed in Fig. 19, the arm member |34 is attached to the upper part of the slide |32 by a sliding connections@ that the arm 234 can move in and out to follow the cord.` This is necessary because the cord forms a veryr slight angle between the end of the hollow shaft |3| and the plane of the pulley |24. This arm I 34 extends downwardly at its outer end with an eyelet at its lower extremity through which the cord |02 has been passed with the beads |33 and |38 located on its opposite sides.4 With this arrangement, the beads 33 and I 38 can pass over the flanged pulley |24 with the downwardly extending portion of the arm |34 properly following without interering with the pulley. yIt should be noted. that the arm |34 is sufiiciently long to allow for its proper endwise movement. However, the arm |34 has a suitable rectangular cross section so as to be non-rotatably mounted with respect to the slide |32. This is so that theslide will take definite positions with respect to the beads |33 and |38.

At the back of the panel on the bearing and support member |20, is mounted an electromagnetic brake for the cord holding mechanism CHM. This electromagnetic brake includes an electromagnet |40 whichl acts upon a spring biased armtaure |4| (see Figs. 18 and 21). The armature |4| is pivoted at I 42v on a suitable support |43 which also acts as a back stop for the armature. |4| in its biased position. The armature is moved to its biased position by reason of a compression spring |44. At the free end of the armature are two extending rods |45 which pass through suitable holes in the bearing member |20 so as to just clear the back face of the panel |00 when the armaturey |4| is ina deenergized position; butwhen the armature. |4| is actuated to an energized position, these brake members |45are pressed against Vthe panel |00 I9 to create suicient friction to prevent sliding movement of the cord holding mechanism CHM in its slot 2| due either to the spring biased pulley |23 or to other operations of the computer.

The percentage wind mechanism |05 as seen in Figs. 17 and 18 has also been illustrated in a double size view in Fig. 19 with the parts shown in expanded relationships to show more clearly the intended operation. The mechanism |65 is mounted on the lever in such a way as to slide in the slot II|. As above mentioned, the spring I I3 is suitably attached to the face of the member so as to cause the mechanism to be biased toward the free end of the lever |0I. The shaft I 58 to which this spring is attached, is nonrotatably mounted to the bearing or slide portion |50 and extends through a notched wheel |5| and a reel |52 to a plate |53 which is suitably attached to the bearing member |50. |52 and notched Wheel |5| are rotatable with respect to the shaft |58 Ibut are non-rotatable with respect to each other. The reel |52 has in a recessed portion a spring |54, which biases it clockwise so as to provide for the restoration of the cord |02 in a manner later to be described. In this connection, the cord |02 cannot be unwound from the reel |52 while the rachet detent |55 is in its biased position. But the rachet detent |55 can be moved to a disengaged position by energization of the magnet |56 to actuate its armature |51 to a raised position.

The back plate |53 has attached thereto a hollow shaft I3| which extends to the inside of the mechanism such as to allowv the cord to be prop* erly fed to the reel |52. It also extends to the outside of the mechanism to provide for a stop against which the bead I 33 can rest.

At the back of the panel |08 as viewed in Figs. 18 and 20, is a motor |60 which operates a variable ratio friction type gear IBI and through an idler |62 also operates another variable ratio gear |63. The gear |64 attached to the variable ratio friction gear |6| acts through an idler |65 to drive the gear |66 attached to a shaft for driving the cord reel |61. When this reel |61 is driven by the motor, it is driven in a clockwise direction as viewed in Fig. 18, which acts to wind up the cord |02 at a rate corresponding to the lapse of time. In other words, the motor |60 may be a synchronous motor suitably drivenfrom a 60 cycle time adjusted source, so that with the proper gear reductions made in accordance with the length of the tape selected in accordance with the time scale for the holding loop, it will cause a one minute length of cord to be wound up on the reel |61 during the lapse of one minute of time. In other Words, when the computer is set into operation by the controller, this motor |68 is set into operation to measure the stack loss time by accurately shortening the holding loop represented by the cord |02 to the proper length.

At the same time that the cord |02 is being wound on the reel |61 for stack loss time, the friction type variable ratio gear |63 is operated so that it acts through gear |68, idler gear |69 and gear to operate the reel I1| This operation of the reel |1| acts to wind up a cord |12 that passes through the panel |00 over an idler pulley |13 and an eyelet |14 at the pivot point |06 to the percent wind mechanism |05 to which it is attached. In other Words, the operation of the reel |1I by the motor |60 in a clockwise direction as viewed in Fig. 18 causes the per cent wind mechanism |05 to be moved against the bias of The reel spring I3 toward the pivot point |06. The ratio of movement between the gears |6I and |63 can be varied by changing the position of the idler |62 which is effected by the screw thread adjustment of knob |15. When the kno-b |15 is in the position shown, the idler |62 is midway between the limits of its possible movement and represents a l to 1 ratio. This would represent a 100 per cent Wind which, of course, is not ordinarily eX- pected to be encountered, but as knob |15 is moved downwardly, the percentage is gradually decreased until the idler |62 actually fails to contact the friction gear 63. This last position represents a zero per cent of wind, or a no wind condition. IThis variation in ratio is relatively gradual, except in the actual change between some small percentage and zero per cent, which condition can be suitably indicated on the scale.

The driving motor I 60 and fire control magnets |46, |56, |86, |8| and |82 are controlled by circuits shown in detail in Fig. 22. These circuits and the operation of-the computer will be presently discussed in detail, but the operation as a result of the energization of these magnets should rst be noted from a structural standpoint.

The energization of the electromagnet causes the idler gear I 65 to be moved upwardly as viewed in Fig. 20. This disengages the gears |64 and |66 so that the reel |61 is free to rotate except for the friction brake which provides only a limited amount of braking eiect for the purpose of preventing over run of the reel during a restoration of the apparatus to its normal condition by the various biasing springs, as will be discussed later. The brake member |85 is pivoted at |86 and is held in a non-braking position by a spring |81. This spring |81 also acts to hold the idler gear |65 in position to engage the gears |64 and |66.

A similar arrangement is provided in connection with the electromagnet |8| which When energized causes the idler gear |69 to disengage the gears |68 and |10, and at the same time apply the friction brake |89 to the reel |1I. This friction bra-ke is controlled similarly as described for brake |85, in that it only applies a limited amount of friction for the purpose of merely retarding the rotation of the reel |1| at the end of an operation by the various biasing springs as described. However, the electromagnet I 82 operates a spring biased armature |88 to an active position in which it is effective to positively lock the reel |1I in its then existing position by reason of a holding finger engaging notches on the side of the reel 1|.

Referring to Fig. 20, it will be noted that a small crank arm 290 is mounted on the back of the panel |80, biased by spring 29| to the position illustrated. By pushing this crank arm 298 against the bias of spring 29|, the gear |63 is causedto contact gear teeth on the side of gear |18 so that the reel can be manually positioned while the electromagnet |8| is energized causing the idler gear |69 to be actuated to a non-engaging position. This crank arm 290 is used for adjustment purposes, as Will be later described.

Referring to Fig. 22 a push button PBI which has a hold-magnet Rl associated therewith, is used to initiate the operation of the calculating organization; while the operation of a push button PB2 is used to designate when an airplane passes over the outer beacon OB of Fig. 6. A push button PB-R is employed for reset purposesas will be presently described. Y

The control circuit organization of Fig. 22 also inc ludes relays R2 and R3 together with a thermal relay TH. The operation of the relays R3 causes the closure of front contact 2|2 for energizing a single stroke bell B and an indicator light LK.

It islbelieved that the characteristic features of this form of the present invention Willbe best understood by further description being set forth from' the standpoint of operation.

Operation secondary form Under theV initial conditions, the flexible cord |02 assumes a position corresponding to the maximum holding loop for the particular wind conditions for which the slide W and the Q angle are then set. Let us assume that there is no Wind, then the Wind ratio setting mechanism |05 will bev moved to a position on the lever |0| causing the read-out at W to indicate zero which iswhen the hollow shaft |3| is exactly over the pivot'pin |06. This is' eiected by the crank 200 as later described. To hold the Windratio mechanism |05 inA such position, the stop |03 is also moved into' position and the thumb nut tightened. With the Wind ratio mechanism |05 insuch position the particular position of the lever |0| is not important, but for the purposes of this discussion, it' is assumed that the'lever I 0| is positioned at zero Q angle When there is now-ind. Under these conditions, the cordV holding mechanism will be biased to the right so as'to hold the bead |90 against the back of the panel |00 While the spring |54 is holding the bead |33 against the endof the hollow shaft |3|. As above mentioned', the spring |54 is substantially stronger than the' biasing spring for holding the `cord holding mechanism (1l-IM.V The cord |021 is thus held in a position representing the time and configuration of the maximum holding loop, since its length is selected in accordance with a suitable scale as described( in connection With Fig. 1.

Assuming that there is no wind, the Wind ratio setting knob will bein a position representing zeroA Wind. Also, the dial D Will beset at the read-out R to the azimuth of thelanding runway.

When an airplane in the holdingY stack is called out by the controller, thel controlleroperates the push button PBI in-lliig.l 22'Which `closes frontv contact 200 to energize the operating-motor |60 with alternating current from a suitable source. As' above mentioned, this motor is driven atv av constant speed, being preferably of the synchronous motor type so as to accurately measure time In series with the motor'- is a back contact of a relay R3 and the primary winding 202 of a transformer 203.

The flow of current through the primary winding of the transformer 203 causes a current to iioW in the secondary Winding 204 which current is rectified by' rectifier 205V and supplied to the winding of magnet Rl. This electromagnet RI acts to hold thepush button contact 200 in an operated position so that a single actuation of the button PBI by the operator is sufficient to initiate the operation of the motor |60l and cause its continued operation.

Referring to Fig. 20, it will be noted that the motor |60 will drive the variable ratio gear |6| but not the gear |63 because of the zero setting of'tlie'wind per cent knob |15. The operation of the motor thus drives the reel |61 at a rate to cause the proper' amount of the cord |02to be wound up on reel |61 in accordance with the passing increments of' stack loss time. rIhis lcauses the holding loop tobe gradually made smaller with the passing of stack loss time. The cord holding mechanism CHM compensates-for this-*by moving to the left against its biasing means including the pulley |23-(see pulley 33 of Figs. 2 and 4 and related descriptions for details).

When' the airplane leaves the holding stack and passes the outer beacon OB` (see Fig. 6), the pilot reports to the controller who then actuates the push button FB2 which energizes the upper winding of the relay R2. The picking up ofthe relay R2 closes front contact 206 completing a stick circuitV through the lower winding of the relay R2 and. including back contact" 201 of relay` R3.

As soon as the relay R2 picks up, it also closes its' front'contact 208 which energizes the electromagnets ISI, |56, |82 and |40 in series. The energization of the clutch magnet |8|4 for the slide W performs no useful function at this' time since the variable 'ratio'friction gear |63 is not being driven at this time. The energization of the electromagnet |56 acts to release the ratchet Wheel |5| and its associated reel |52', so'that the continued operation of the reel |61 may.l draw cord |02 at a rate in accordance with the elapse of time. However, it should be noted that at this time the cord holding mechanism CHM is locked in position by reason of the energization of the electromagnet |40, so that the position of the cord holding mechanism CHM is not changed during this part of the operation.

It should be noted that theA energization of the electromagnet |82, although it locks the reel |1| in its existing position, performs no useful function at this time, since the reel |1| isnct being driven.

Since the cord |02 has been reduced in-length equal tof the stack-loss time by the winding of the cord onto the reel |51 in accordance With `the lapse of time, as soon as the pilot of the airplane reports passing over the outer beacon OB; the controller can read the azimuth of the out-time course from the dial D at the readoutA P- This information is immediately communicated to the pilot of the airplane so that h e can begin the out-time course of the holding loop at once; At the same time, the controller actuates the push button PBZ, Which energizes relay R2 (see'Fig. 22).

Th'e'motor |60 continues operation so as to cause the cord |02 to be wound up on the reel |61 in accordance with the'lapse of time. But because the cord holding' mechanism CHM is locked by the electromagnet |40,` the cord 02 begins to be iinwound from the reel |52. This can be done because' the ratchet |55 is released by magnet |56. ThisV causes the bead |33 on the cord |02 to begin to travel toward the pulley |24. The time consumed by the bead |33 in travelling fromthe hollow shaft |3| tothe point of'tangen'cy With the perieh'ery of the pulley |24. represents the time of the out-time course of the holding loop. The slide |32 is `also moved by' the head |33 along the rod |30 to a point Where it operatesV the contact spring |35 to make connection between the terminals '|33 and |31 when the bead |33 reaches the point'of tangency. Since the rate of travel of the bead |33 corresponds to the timescale for the flexible cord |02, the time which elapses following the actuation of the push button PBZ? to the time that the contact |35- is closed, corresponds'y to the out-time.v

The closure of contact |35 closes' a circuit to pick up the relay R3 by energizing its upper winding. The picking up of this relay R3 closes front contact 209 to close a stick circuit for the relay R3 through its lower winding, a resistor 2|0 of the thermal relay TH and a contact 2|! of the thermal relay. The opening of back contact 20| immediately deenergizes the motor |60 and stops its operation. The closure of front contact 2|2 of relay R3 closes a circuit for a bell B and alamp LK. Thus, the termination of the out-time is both visually and audibly indicated to the controller who immediately advises the pilot of the airplane to begin the right-hand procedure turn. In this way,` the mechanism automatically measures the stack loss time and the out-timefor the controller.

The picking up of the relay R3 also closes front contact 2|3 to energize the electromagnet |80 to declutch the motor from the reel |67. The opening ofthe make-before-break back contact 2|4 deenergizes the electromagnetic lock |82 for the slide W as well ,as the electromagnetic lock |40 for the cord holdingmechanism CHM. However, the closure of the make-before-break contact 2|4 completes a circuit for the magnets |56 and |8| through front contact 2 l5 and resistor 2 I6. These contacts 2|4 and 2|5 are so adjusted that there is no interruption in the energization of these magnets during the picking up of the relay R3. This maintains the locking detent |55 out of contact with the ratchet wheel |5| and also maintains the reel declutched from the motor for the restoring operation.

With these conditions, the spring |54 winds up the cord |02 on the reel |52 until the bead |33 is again restored to normal position against the hollow shaft |3I. This operation of course unwinds any cord on the reel |61 until the bead |90contacts the rear side of the panel |00. yThe release of'the brake |40 allows the cord holding mechanism CHM to tend to assume a right hand position to tighten yup the cord |02. As previously mentioned, the bias 'of spring |54 is substantially stronger than the bias for cord holding mechanism CHM, so that the cord holding mechanism CHM is caused to assume 'a position `in accordance with the maximum holding loop forno stack loss time under the conditions for which the computer is then set.n

It should be noted that the picking up of the relay R3 opens back contact 201 included in the stick circuit of the lower winding of relay R2,

ywhich allows the relay R2 to be released to assume its normal deenergized condition.

After an interval of time measured by the heating time of the thermal relay TH which is sufcient for the computer to be restored to normal, the contact '2H opens and deenergizes the stick circuit for the relay R3 which releasesy and restores the electromagnets |56, |80, and |8| to normal deenergized positions.

It is noted that while the cord' |02 is being restored to its original position, the magnet |80 keeps the reel |61 declutched from the motor |60 so as to readily allow such restoration, the friction brake |85 is provided in order to prevent the pulley |61 from overrunning by reason of stored momentum.

When there is a wind condition, the drift angle and Q angle are found in a manner previously described in connection with Fig. 9. The dial D is set at the azimuth of the runway plus or minus the drift angle in accordance with the description provided in connection with Fig. 1. The lever v |0| is set at thepproper Q angle either right or left in accordance with the direction of the Wind. In other words, as soon as the direction and speed of the wind is known, the dial D and the Q angle may be directly set. Also, when the speed of the wind is known, its percentage Vis foundfwithrespect to the selected cruising speed for performing of the landing procedure.4 This percentage is used to set knob |75, and from the chart of Fig. 10 the setting of the scale W on the arm |0| is found for Zero stack loss time for that percentage wind. When the setting for the percent wind mechanism |05 is determined from the chart, the thumb nut on the stop |03 is loosened and moved until the proper setting appears at the read-out W.

This is accompanied by the artificial energization of the electromagnet |8| by operation of push button PB--R to declutch the reel after the resetting operation of stop |03 has been performed, so that by operating the hand crank 290 the reel can be manually positioned to take up the slack, if any, in the cord |l'2. On the other hand, it may be that the' setting operation for the slide |05 requires that it be moved outwardly along the lever |0| in which case merely the release of the reel |l| from its connection with the motor will allow the biasing spring I3 to draw out the necessary amount of the cord |12.

In this way all of the settings of the calculator in accordance with a particular existing wind condition are made prior to calling the airplane from the holding stack.

In the above description, no particular settings have been given for this secondary form of the computing organization, because it should readily be appreciated that the holding loop is formed in the same manner and with same scale relationships as described in connection with Fig. 1. This form of the invention gives the same solutions to the different problems to which it is subjected, as are given by the primary form of Fig. 1. This secondary form of the present invention is shown more particularly for the purpose of illustrating that the stack loss time can vautomatically be put into the computer and that the measurement of the out-time can be automatically effected.

Referring to Figs. 17 and 18, it will be noted that the `setting of the wind slide |05 to the zero position at the read-out W, causes the maximum holding loop to be represented by the mechanism for no wind conditions. It is noted under these conditions that the'length of the cord |02 would accordingly be proportional to the length of the actual holding loop assuming that the cord extended from the point |06 over the pulley |24 and back to the point |06. However, for convenience in the structure, the cord |02 is foreshortened and taken over the pulley |47 with a suitable bead attached thereto at a point to determine that the pulley |24 assumes the same position as if the cord |02 were actually taken to the point |06. This shortening of the cord |02 does not in any way affect the proper calculation of the quantities involved.

In some cases, it may be desirable to have a different holding loo-p time, and this different time may be employed by merely positioning the bead |90 to a new position adding or subtracting the proper length of the cord |02 in accordance with the time constant scale employed. If it is desired to have the calculating organization adapted for use in connection with different holding loop times, the bead |90 may be so at- 25 tached to the cord |02 as to be adjustable to different calibratedy positions on the cord 102.

In the description of the invention in its different forms, consideration has been given more particularly to the calculating functions of the apparatus employed, but it should be definitely understood that the computer of the present invention is contemplated for use more particularly in the calculation of holding loops in connection with a landing procedure as previously described, and that these calculations and operations are for the purpose of landing airplanes at equally spaced time intervals regardlessY of their locations in the holding stack. For this reason when a calculator is used as disclosed in the secondary form, it may be necessary to employ several such computers. This is because any one computer is allotted to a particular airplane until that airplane has begun its procedure .turn for the holding loop. If the airplanes are to be landed at relatively close time intervals, it might be that the second airplane should be started on its landing procedure before the rst computer for the first airplane has completed its operation. In other tvc-rds, it may mean that several computers of the type described Inay be required in an actual installation.

M athematioal rsume' The purpose of this portion of the specification p is to show that the operation of the computer of the present invention is mathematically correct. For this reason, attention will be now specically -directed to the kinematical problem involved in a holding loop maneuver forming part of a landing procedure according to the principles of the present invention.

In performing the landing procedure, there are certain basic factors and instrumentations involved which `may be enumerated as `follows:

:y V(l). The'landing procedure, including the hold- .ingd loop maneuver isvperformed ata constant speed relative to the body of air through which the airplane is passing as shown by an airspeed indicator on the airplane.

(2) The heading of the airplane is indicated by a compass of suitable type located on the airplane so that instructions received by the pilot as to the heading of the out-time course can be followed.

(3) rllhe airplane is provided with ysuitable navigational equipment, such as an automatic direction nder, so that the airplane can follow the in-time course defined by the inner and outer radio beacons IB and OB respectively.

' (4) The airplane is provided with a rate of turn `indicator so that it can make the desired circling maneuvers, such as performing a :procedure turn at 3 per second, or 1r/60 radians per second.

(5) The approach controller is provided with suitable timing means so as to be able to measure the stack loss time and also the out-time when it has been calculated.

(6) The approach controller is provided with a computer Constructed in accordance with the principles of the present invention as above described.

(7) A suitable holding stack and holding loop pattern is selected to constitute the landing procedure as above described.

System of notation For the purpose of expressing the various vfactors and terms of the problem, the following conventions and notations are employed:

1J=Airplane speed with respect to the ground w=Wind speed 1L=The airspeed of the airplane T=Total time required for landing procedure (includes the time from the call of the airplane from the holding stack until it passes the outer beaconon the inward course toward the runway) ts=Time which elapses between the call of the airplane and the time it passes the outer beacon OB (abbreviated: stack` loss time) t='I'ime duration ofthe complete holding loop t1=Tirne duration or" the out-time course designated OT (out-time course with respect to the moving body of air) t2=Time duration of the in-time course designated IT (in-time course with respect to the moving body of air) p=Number of radians through which the airplane turns per unit of time in the procedure turn. (Assumed to be 1r radians per minute) Q=The acute angle between the ground course on the approach to the runway and the reciprocal of the direction of the wind.

c=A constant factor with dimensions of speed (such as six inches per minute) e=The acute angle between the out-time course and the reciprocal of the in-time course L=Total length of actual path of the airplane in the holding loop L1=Total length of simulated path of airplane in construction D=Total displacement ,of moving body of air in time t.

Special symbols (1) `A small letter underlined is used to denote a vector having direction and magnitude, but a small letter without the underlining will denote only the magnitude of the vector.

(2) Small letter subscripts z' and f will be used to characterize the terms as belonging to the uttime course and the in-time course respectively. For example, the vector term ui is referred to as the initial velocity of the airplane relative to the moving body of air (initial because it relates to the out-time ilight). Also, the vector term of is referred to as the iinal velocity of the airplane relative to the ground (final because it relates to the in-time ilight).

Statement of the problem Given: A holding loop time t, the airspeed of the airplane u, the wind velocity w, and the direction only of the in-time course of the airplane ce which is the direction of the axis of the runway course. Y

vTo nd: The value of time t1 of the out-time course and the direction of ui conveniently termed the initial heading, which such related values that the time t will be exactly consumed in the holding loop maneuver and so that the heading of the airplane, when it reaches the axis of the runway at the end of the procedure turn of the holding loop, will be such that the track of the airplane is parallel to and coincident with the axis of the runway course.

Solution Ais understood that Vthe stack loss time is measured Fig. 23 shows certain relationships between the system of notation given aboveand the actual ground course of an airplane under the conditions shown and described with respect to Fig. 15.

Fig. 24 is a construction of the holding loop simulating the actual course of the airplane in a moving body of air and constructed in accordance with the principles of mathematical analysis and related to the ground course of Fig. 23.

Since the speed of the airplane relative to the body of air is assumed to be constant throughout the landing procedure as measured by the air speed indicator, the following equation is true:

Referring to Fig. 23, the direction only of the vector vf, the length u only of the vector uf, and

both th-e direction and magnitude of thevector w are known. The standard construction for obtaining the direction of uf under these conditions has been described abdve in connection with Fig. 9 and will not be discussed in detail at this time. By performing this construction, the complete vector uf and the Q angle are to be regarded The presence of the wind causes the problem to become involved for two reasons:

(l) The track of the airplane with respect to ground during the procedure turn is not a true circle but is a segment of a trochoid.

(2)'Ihe ground speed of the airplane is a function of position along the loop. Thus, while the airplane speeds ci and vf are constant, they are not equal to each other; and along the procedure turn, the ground speed varies from point to point.

These difficulties are resolved at once by referring the motion of the airplane to a coordinate system moving with the air, instead of the coordinate system flxed with respect to the earth.

Because the air speed u of the airplane is held i constant throughout the holding loop maneuver and the rate of turning in the procedure turn is held constant, the procedure turn referred to the moving coordinate system is a true circle with a radius of ALL/p and the increments of length along the trajectory of the airplane are at every point strictly proportional to the increments of time.

Let us consider the wind condition which applies to Fig. 15. To an observer in a balloon which is over the outer beacon OB at precisely the time the airplane also passes over the outer beacon OB to execute the holding loop maneuver, it appears that the airplane has an initial velocity u1 and that the outer beacon OB is also moving away from the balloon with a speed and direction represented by the vector -w. The path of the airplane is so proportioned that after it makes a circular turn at the rate p while traveling at the speed u and then proceeds along the inbound straight away with a velocity of uf, the observer in the balloon sees the airplane pass 'once'more directly over the outer beacon OB which throughout the maneuver has been moving along a straight line with respect to the balloon with the (lll , 28 velocity of -w. In other Words, the balloon which was ovethe outer beacon during the first passing of the airplane over the outer beacon is now a distance away from the outer beacon eX- pressed by the following equation:

(5) D=wt In' brief, the course of the airplane consists of two straight line segments and a circular portion with the straight lines being tangent to the circle and open at the other ends by a distance equal to the length D of the path of the balloon above described. The motion of the airplane with respect to the ground is as if the airplane were flying within a large box containing still air and its contentswere being carried along over the ground with the velocity of the wind.

Let us now consider a miniature construction of the actual trajectory of the airplane relative to the moving body of air. The length L of the actual physical path of the airplane in the moving body of air is represented by:

(6) Lzut But since it is desired to construct the trajectory of the airplane on a reduced scale, let us choose a scale factor c with the dimensions of speed so that the length L1 of the construction of airplane path of Fig. 24 is represented by In fact, the ratio of any length in the construction to the corresponding length of the actual path is equal to c/p. For the purposes of the construction of the actual calculator or the gures of the drawings, any suitable value may be assumed for the factor c.

Referring to Fig. 24 choose a point OB and lay ofi to scale the displacement wt of the moving body of air. This displacementl D in the construction of Fig. 24 has a length ct(w/u). Through the terminal point OB1 of the vector -wt draw a line to the point F parallel to the veor uf of Fig. 23. This gives the direction of the final air velocity of the airplane relative to the air for the in-time course of the holding loop.

The circular turn included in the maneuver has a radius given by the expression ul/p which is the ratio of the airspeed to the rate of turning. The radius of this circle to scale is therefore c/p. This circle must be drawn tangent to a line through OB1 and parallel to the direction of -ui with such e, position that when a line is draw?! tangent to the circle through the point OB, the total length of the line from OB to the point of tangency G, plus the length from G around the circle to F, and plus the length of the line from F to OB1 equals the scale distance et which is proportional to the actual distance ut travelled by the airplane during the total holding loop maneuver. When this condition concerning the length of the trajectory is met, the construction just described represents to scale, the path of the airplane relative to the moving body of air, and is related to the fixed coordinate system by the angle between the line from OB1 to F and the 

